1. Field of the Invention
This invention relates generally to the field of aircraft structural systems and more particularly to a rib structure and attachment system for composite wing panels.
2. Description of the Related Art
In aircraft structures, wing panels, which consist of skins and stringers, react wing bending loads. These loads and the resulting deflections produce upper wing compression buckling and a crushing load on ribs supporting the wing panels. The compression buckling capability for the panel is driven by geometry, rib spacing and stringer spacing. The boundary conditions for the panel are determined by the method of support the rib gives the skin/stringer.
Traditional aluminum panel design as shown in FIG. 1 provided panel support by attaching the rib 10 to the stringer 12 by means of a series of rib bolts 14 between the free flange 16 of the stringers and the associated rib chord flange 18. Skins 20 are attached to the stringer outer flanges 22 using fasteners. An alternative method is to attach a butterfly clip between the stringer web and the rib chord. These attachments provide column stability for the panel and do not let the stringer roll over. These designs are undesirable because they require installation while the wing box is being built. Drilling holes inside an enclosed wing box presents many challenges and provides a source for costly rework.
Further, if this rib bolt design is applied to a composite wing structure, it creates interlaminar tension problems in the stringer radius. This is a poor load path for the composite structure which may require reinforcement methods for the stringer radius adding more cost. The composite wing also needs disbond affestment fasteners common to the stringer and skin in addition to the rib to stringer attachment.
It is therefore desirable to provide structural elements that provide an improved load path for rib support of wing panels. It is further desirable that the structure not require drilling of holes inside an enclosed wing box.